MicroRNAs (miRNAs) are a new class of non-coding small RNAs that negatively regulate gene expression by either degrading mRNA or inhibiting protein translation. miRNAs have been shown to play very important roles in a variety of diseases, such as cancers, viral infection, genetic disorders, and cardiovascular diseases. Recently we found that miR-21, an oncogenic miRNA gene was aberrantly overexpressed in a variety of cancers, was also upregulated in the mouse cardiac hypertrophy model and rat carotid artery balloon injury model. Knockdown of miR-21 induced apoptosis in vascular smooth muscle cells and in the rat carotid artery balloon-injured model by targeting the 3'untranslated region (UTR) of the phosphatase and tensin homolog (PTEN) gene and indirectly regulated Bcl-2 gene expression in vascular smooth muscle cells (VSMCs). To further understand the molecular mechanism by which miR-21 regulates gene expression on the important signaling pathways, which play pivotal roles in vascular diseases, we constructed a lentiviral vector in which the miR-21 gene was driven by the rat smooth muscle cell specific promoter (rSM22) and generated a transgenic rat model in which miR-21 is overexpressed in VSMCs. We found that several transgenic rat founders display consistent phenotypes: growth retardation and slightly paralyzed hind limbs. This transgenic rat model will certainly provide insight to understanding miRNA functions in cardiovascular diseases and will help us further evaluate potential applications of miRNA in diagnosing and test miRNA based therapy for cardiovascular diseases. PUBLIC HEALTH RELEVANCE: This proposal is to characterize transgenic rats expressing miR-21 using lentiviral vector to address the biological functions of miRNAs by targeting miR-21 gene into vascular smooth muscle cells. The phenotype and molecular mechanisms underlying the phenotypes will also be examined using this transgenic rat models by investigating how miR-21 is involved in the posttranscriptional regulation.